Apply suggestions by @jricher.

Author: msporny

index.html

@@ -561,15 +561,19 @@ <h3>Use Cases and Requirements</h3>
         </p>
 
         <p>
-While digital proofs, a subset of which are digital signatures, are required
-to ensure the protection of a <a>verifiable credential</a>, this specification
-does not standarize on any single digital signature format. At the time of
-publication, Working Group members had implemented
+Digital proof mechanisms, a subset of which are digital signatures, are required
+to ensure the protection of a <a>verifiable credential</a>. Having and
+validating proofs, which may be dependent on the syntax of the proof
+(for example, using the JWS of a JWT for proofing a key holder), are
+an essential part of processing a <a>verifiable credential</a>. At the time
+of publication, Working Group members had implemented
 <a>verifiable credentials</a> using at least three proof mechanisms:
 JSON Web Tokens [[JWT]], Linked Data Signatures [[?LD-SIGNATURES]], and
 Camenisch-Lysyanskaya Zero-Knowledge Proofs [[?CL-SIGNATURES]]. The group
 expects some of these mechanisms, as well as new ones, to mature independently
-and become standardized in time. One of the goals of this specification is to
+and become standardized in time. Given that there are multiple valid
+proof mechanisms, this specification does not standardize on any
+single digital signature mechanism. One of the goals of this specification is to
 provide a data model that can be protected by a variety of current and future
 digital proof mechanisms. Conformance to this specification does not
 depend on the details of a particular proof mechanism; it requires clearly